1. Field of the Invention
The present invention relates to molds used to form products, such as monitor casings and engine blocks, and, more specifically, to a mold having a core for creating indicia markings in formed products that is easily changeable with another core when it is necessary to change the content of the indicia.
2. Background Art
Molds with removable inserts for mold frames are in use and are especially valuable for prototype or low production molding needs that require the tooling be changed after relatively short runs. However, the known molds of this type still require substantial changeover time and the need exists for an inexpensive mold system requiring minimal changeover time and machining operations.
Monitor housings are formed through an injection molding process that often uses indicia markings to identify the type of plastic used and the grade of plastic. An injection molding system, may use both a mold and an injection molding machine. The mold contains a core mold and a cavity mold. The cavity mold contains a cavity that is filled with molten resin that is injected through a nozzle. The core mold is inserted into the cavity mold causing the outer surface of the core mold to slide flush inside of the inner surface of the cavity mold. A cavity is formed between the core mold and the cavity mold when the two molds are fully engaged together. Top and bottom clamp plates are mounted on the back surfaces of the core mold and the cavity mold, respectively. A locking member is fixed to each of the two clamp plates to secure the two molds prior to beginning the molding process. The locking member is then removed prior to separating the molds to extract the product.
The injection molding machine may be constructed using a hopper that is mounted to the rear end portion of a longitudinal heating cylinder. Molten resin is introduced to the heating cylinder via the hopper. The heating cylinder heats the molten resin using a heating means to maintain the molten state of the resin while feeding the resin into the mold. A rotatable screw is axially positioned in the heating cylinder and the cylinder is connected to a motor via a reduction gear. Thus, the screw is rotationally driven by the motor. The screw plasticizes the molten resin, acts as a typical plunger, and is operated by a cylinder actuator.
To form a product, such as the front and rear housings for a monitor, using the above injection molding system, molten resin is introduced into the heating cylinder through the hopper. Then, the resin is fed to the front end of the cylinder while being heated and plasticized by both the cylinder and the screw. In the front end of the heating cylinder, the molten resin is pressurized by the screw prior to being injected into the cavity formed between both the core mold and the cavity mold. The molten resin travels from the heating cylinder into the cavity via the nozzle of the cylinder and the sprue of the top clamp plate of the cavity mold. The molten resin in the cavity is then formed into the desired product that has a shape that corresponds to the shape of the cavity.
It is often preferable to create a stamped figure or letter indicia on the product to indicate either the manufacturer or the material of the product used during the injection molding process. To create the desired stamp on the injection molded product, an indicia forming segment may be integrated with the core mold in a position facing the cavity.
However, using an integrated indicia forming segment is problematic in that it is very difficult to change the content of the indicia. Thus, when it is necessary to change the existing content of the indicia, the existing content of the indicia has to be removed from the section through a grinding process prior to securing the new content on the portion. Therefore, the integrated indicia forming portion reduces work efficiency in the changing of the content of the indicia and increases the production cost of the products.
It is often necessary to stamp an indicia that indicates the kind of resin used, onto the surface of a molded product. Furthermore, it is not uncommon for a manufacturer to selectively use two or more kinds of resins in any particular injection molding process. Thus, necessitating a different indicia forming segment for each type of plastic or composite used. To allow multiple combinations or types of plastic to be used without introducing long delays to change the indicia forming segment, a rotary core can be used that has an arrow mark that can be oriented to indicate the type of resin that was used to form the product. For example, when one of two kinds of resins, ABS resin and ABS+PC resin, is selected for use in an injection molding process, a rotary arrow is oriented so that the stamp will show the arrow pointing to the appropriate resin identifier. The indicia forming segment has two stamps, one having the indicia ABS and the second having the indicia ABS+PC. The indicia forming segment is attached to the core mold and contains a rotary core that has an arrow mark that is rotatably mounted in the core mold at an intermediate position between the two stamps. When the resin used in the injection molding process is changed from one of ABS or ABS+PC to the other, the rotary core is rotated by a user to indicate the kind of resin used by aligning the arrow with the appropriate indicia. A rotary core that uses an arrow mark may also be used to indicate the grade of a resin used in the injection molding process. For example, if a manufacturer were using the three grades of resins C 2950, O 812 and O 810 alternatively in different injection molding processes, three stamps could be oriented around the rotary core to enable easier changing of the identification of the resin a product is constructed with.
Some developments in changeable core technology are shown, for example, in U.S. Pat. No. 4,210,196 to Weiner entitled Die Casting Apparatus and U.S. Pat. No. 4,828,479 to Pleasant entitled Molding Apparatus. Contemporary indicia forming segments using a rotary core can be problematic in that having multiple stamps on one product make it more difficult to read the indicia and reduce the competitiveness of the product.
I believe it may be possible to improve on the art of indicia forming segments by providing an indicia forming segment that can be easily changed, that can create more complicated labels than that typically created with rotary cores, that can be easily changed with another indicia marking section, that improves the manufacturing efficiency of producers by reducing the amount of time necessary to change indicia forming segments, and that increases the amount of information that can normally be conveyed with an indicia forming segment.